Taiwan patent publication No. 568160 disclosed “structure of fireproof doors” is relevant to a fire door lock. Two latch bolts are disposed at an upper end and a lower end of a fire door separately, and the latch bolts can be blocked by two stoppers disposed at a door frame therefore forming a lock state. Usually, the blocked latch bolts departs from the stoppers and leads to an unlock state via actuation of a main lock. With reference to FIG. 1, a fire door lock comprises a latch structure 20 disposed at a fire door 10 and a stopper 40 disposed at a door frame 40. The latch structure 20 comprises at least a lock base 21 and a latch tongue 22 having a blocking surface 23 and a restraining surface 24 opposite to the blocking surface 23. The latch tongue 22 is swingably disposed at the lock base 21. Once the latch structure 20 and the stopper 40 are situated in a lock state, the blocking surface 23 of the latch bolt 22 may contact against the stopper 40 to prevent the fire door 10 from being opened. Once the latch structure 20 and the stopper 40 are situated in an unlock state, the latch bolt 22 is actuated by a main lock (not shown in Figs.) to shrink into the lock base 21. At this time, the latch bolt 22 is not blocked by the stopper 40 to enable the fire door 10 to be opened. With reference to FIG. 2, when the state of the fire door 10 is switched from the unlock state to the lock state, the latch tongue 22 can not be actuated by the main lock to enable the latch tongue 22 to still protrude from the lock base 21. In this moment, the latch bolt 22 must pass through the stopper 40 to form a lock state. Generally, the fire door 10 is actuated by a door closer (not shown in Figs.), once the thrust of the door closer for driving the fire door 10 is insufficient, the stopper 40 contacts against the restraining surface 24, and eventually an unlock situation is formed between the latch structure 20 and the stopper 40. Therefore, the fireproof and burglarproof functions of the fire door 10 will be all lost via incapability of closing the fire door 10.
Besides, referring to FIG. 1, by using appropriate tools, the latch bolt 22 of the latch structure 20 can be easily pushed and shrunk into the lock base 21 by a thief to form an unlock state between the latch structure 20 and the stopper 40. Therefore, the burglarproof function will be lost.